Synchronized multi-user multi-carrier communications technology (e.g., high speed wireless or Digital subscriber line (xDSL)) has developed in recent years in response to the demand for high-speed Internet access. For example, in wireline communication systems, xDSL technology utilizes the communication medium of pre-existing telephone systems. Thus, both plain old telephone systems (POTS) and xDSL systems share a common line for xDSL-compatible customer premises. xDSL systems (e.g., Very High Speed DSL or VDSL systems) involve multicarrier transmission over cable bundles formed by multiple copper pairs, where each pair typically services a different customer.
Likewise, wireless communication systems include multiple communication channels over which multiple carriers having information are transmitted. In wireless channels (like, cable bundles of wireline channels), electromagnetic phenomena typically create interference between users, among which far-end crosstalk (FEXT) may significantly compromise system performance. FEXT noise, as seen by a user of interest (referred to as a victim user) depends on the signal transmitted for each of the other users (referred to as disturbers) as well as the electromagnetic coupling between neighboring channels and/or cable pairs carrying the victim user's and disturbers' data.
Traditionally, high speed wireless and wireline systems (e.g., xDSL) do not account for FEXT noise coupling and disturber modulation information, as the only information taken into consideration in determination of spectral efficiency of the communication system is the Signal-to-Noise ratio (SNR) derived from a measurement of the variance of the aggregate noise under the assumption of the noise being Gaussian. In particular, conventional wireless and wireline systems (e.g., xDSL) compute bit loading metrics based on an Additive White Gaussian Noise (AWGN) model having a variance that is proportional to the inverse SNR measured. However, such exclusive reliance on AWGN models may lead to inaccurate computation of bit loading and/or SNR margins. This sub-optimum computation is not just observed in a wireline xDSL system in which multiple users are synchronized, but is observed in all synchronized multiuser multicarrier systems that suffer from self-FEXT noise from synchronized disturbers, be it wireline or wireless communication systems.
Therefore, what is needed is a more accurate noise model for characterizing a communication system that does not rely only upon AWGN models and takes into consideration FEXT noise and disturber modulation effects.